test: lock in 7-day free trial copy (closes #2290)

[vivekchand]

Closes #2290.

What

Adds a regression test that locks in the 7-day free trial copy across user-facing surfaces. The 14→7 migration is already complete in code (PRD matrix, paywall modal, dashboard.py gate copy, alerts/approvals/notifications templates). This PR adds the guard so a future copy-paste from old marketing material can't quietly reintroduce "14-day" trial language.

How

tests/test_trial_copy_consistency.py scans the user-facing files (PRD.md, dashboard.py, clawmetry/sync.py, clawmetry/templates/partials/paywall_modal.html, clawmetry/templates/tabs/{alerts,approvals,notifications}.html) and asserts four invariants:

1. No "14 day" / "14-day" appears within 80 chars of "trial" in any user-facing surface (tests/, CHANGELOG, etc. are excluded — they can legitimately reference history).
2. The PRD pricing matrix line for Trial lists 7 days.
3. The paywall modal CTA reads "7-day free trial".
4. dashboard.py mentions "7-day free trial" in ≥ 2 places (Pro-gate error + cloud upgrade link).

Verified the regression catches real flips

$ sed -i 's/\*\*7 days\*\*/\*\*14 days\*\*/' PRD.md
$ pytest tests/test_trial_copy_consistency.py::test_no_14_day_trial_copy_in_user_facing_files
FAILED — Found '14-day' near 'trial' (issue #2290):
  PRD.md:34 -> '... | **Trial** | — | **14 days**, all Pro feature...'

Acceptance criteria from #2290

• grep -rIn "14[- ]day" returns zero hits in trial contexts (only 14-day token-usage chart references remain — unrelated)
• grep -rIn "7[- ]day" covers all trial mentions
• PRD matrix reflects 7-day trial
• Cross-references companion cloud issue (link to follow) — vivekchand/clawmetry-cloud#1210 tracks the cloud-side TRIAL_DAYS + Stripe trial_period_days flip

Test plan

• pytest tests/test_trial_copy_consistency.py -v → 4 passed
• Flip PRD back to "14 days" → test fails with the offending file:line pinpointed